The present invention relates to a method of cleaning the rotor of a rotor spinning machine in which, after the opening of a spinning unit, there are sucked off from the rotor fibres and impurities released from the inner surface of the rotor by pressure air applied to said inner surface. The invention also relates to a device for carrying out the method.
In rotor spinning machines, the transformation of singled out fibres into yarn, in particular in the production of cotton yarn, involves the collection of impurities on the collecting surface of the rotor. Impurities consisting mostly of plant rests are comprised directly in the sliver, get released in the singling out process, and some of them get into the rotor. In the rotor, some of the entering impurities are retained in the fibre band and subsequently in the yarn produced by the fibre band twisting and leaving the rotor. The remaining impurities stick in the rotor, cling to its inner surface, and can cause ruptures of the yarn being spun. Together with the impurities, remaining in the rotor is also the part of the fibre band that has not been transformed into yarn, and a number of singled out fibres that have entered the rotor from the singling out device before the spinning unit stops after a yarn rupture, whatever may have been the yarn rupture cause.
For this reason, before any attempt at reinstalling the spinning process at a spinning unit affected by yarn rupture, the inner space of the rotor must be cleaned to restore the yarn production conditions.
The rotor can be cleaned manually or by automatic means which can be either a component part of each spinning unit, as disclosed for instance in the CS 219 283 (CH 5935/79), or provided on an attending device adapted to move along the working places of a rotor spinning machine.
In a well-known attending device, the fibre band is sucked off from the rotor through a tube connected to an underpressure source and adapted to deliver the fibre band from the rotor into the attending device. Concurrently or subsequently, inserted into the rotor are mechanical means, such as a needle or a brush, intended to remove deposited impurities from the collecting groove of the rotor.
Thus is arranged for instance the cleaning device disclosed in the inventor's certificate CS 234 432 featuring a revolving sucking-off tube fitted with a revolving drive and adapted to be inserted into the rotor. In the operating position of the cleaning device, the circumference of the revolving sucking-off tube is in contact with the inner edge of the rotor mouth positively sharing the revolving motion of said tube. Simultaneously with the revolving sucking-off tube, a mechanical cleaning device moves into the rotor consisting of a cleaning brush and serves to clean the collecting groove of the rotor,
The drawback of this arrangement consists in the positive rotation of the rotor during the cleaning. This causes fibres existing in the rotor to get wound on the rotating sucking-off tube, which are apt to cause failures.
This drawback has been removed by the cleaning-device disclosed in the inventor's certificate CS 240,753 requiring no rotor rotation during the cleaning because into the rotor there is inserted a rotating brush whose cleaning elements are in diameter superior to the maximum inner diameter of the collecting groove of the rotor. The rotating brush is rotatably seated in a cleaning head in which is provided also a suction-off aperture connected to an underpressure source for sucking off the fibre band and impurities from the rotor.
Mechanical cleaning means have a number of drawbacks consisting especially in the contact of the rotor with a foreign solid body, resulting either in excessive wear of the cleaning means or, if the cleaning means are too hard, in damage to the rotor. Once worn, the cleaning means are unsuitable to clean the rotor, and must be either replaced by new ones or adjusted. The contact of the cleaning means with the not yet stopped rotor may provoke sparking involving the risk of ignition of the lint around the cleaning area. Small diameter rotors lack space sufficient for simultaneous sucking off of the fibre band and inserting of the mechanical cleaning means into the rotor.
Also known is pneumatic cleaning of the rotor comprising the sucking off of the fibre band from the rotor with simultaneous or subsequent application of a pressure air stream to the soiled parts of the inner surface of the rotor.
Simpler is the pneumatic cleaning of passive rotors, i.e., those in which a rotor having no ventilation holes is seated in an underpressure chamber. Such passive rotors can be cleaned without opening the spinning unit, just by supplying a pressure air stream into the rotor, as disclosed for instance in the DE OS 27 35 311 in which two jets provided in the cover of the underpressure chamber lead into the inner space of the rotor two streams of pressure air, one of them directed to the collecting groove of the rotor and the other to the inner circumference of the rotor. The two streams of cleaning air are led into the rotor under different angles with respect to the tangent lines passing through the points of their incidence on the inner circumference of the rotor. The fibres and impurities are in this arrangement sucked off across the edge of the rotor into the underpressure chamber. Such rotors can be cleaned in the same way also in the open state of the spinning unit, with the jets arranged in a cleaning device adapted to be put in contact-like vicinity of the rotor.
The effectiveness of this arrangement is based on the fact that the rotor turns; consequently, it cannot be used in active rotors producing underpressure by their rotation because they are fitted with ventilation holes.
Such active rotors can be cleaned in the stopped state only by opening the spinning unit, sucking off the fibre band through a tube, putting to the rotor a head fitted with a pressure air jet revolving around the rotor axis and leading the pressure air stream onto the soiled surface parts of the rotor. However, part of the pressure air with some impurities gets out into the surrounding space. Another drawback consists in the risk of the fibres getting wound on the revolving jet body and thus locking it.
Another well-known device is disclosed in the inventor's certificate CS 234 501. After the opening of the spinning unit, a cleaning head is placed to the rotor comprising a channel for removing impurities connected to an underpressure source, stationary lets for pressure air supply, and an open channel for ambient air supply.
Such a device can be used only in large-diameter rotors, which nowadays, are not generally used due to the increasing r.p.m. speed. Besides, such devices can remove the fibre bands from the rotor, but not impurities clung to the inner surface of the rotor.
In all the above mentioned methods of pneumatic rotor cleaning, there is a tendency of the pressure air supplied to the rotor to get out from the rotor inner space across its edges involving the risk of fibres and impurities getting out into the ambient space. In some of them, there is also a risk that the fibre band escapes, subsequently getting into the machine and possibly causing a failure in it.